1. Field of the Invention
This invention relates to a continuous process for encapsulating agricultural chemicals, biopesticides, food constituents, medicaments, and other biologically active agents for controlling their release and protecting them from degradation due to environmental exposure and to the compositions prepared thereby.
2. Description of the Prior Art
Various approaches to the controlled release of chemical biological active agents by means of a starch-based encapsulating material have been disclosed previously. Some of these methods have involved the use of chemical crosslinking reactions. In U.S. Pat. No. 4,382,813, Shasha discloses a system for encapsulating certain types of pesticidal agents by the rapid insolubilization of a starch-containing material alkoxide with a bivalent cation selected from the group of calcium, barium, and strontium. While this system is applicable to water-insoluble agents, it is not particularly suitable for those which are water soluble, nor for substances susceptible to alkali degradation.
In U.S. Pat. No. 4,439,488, Trimnell et al. disclose a method of encapsulation wherein entrapment is achieved by insolubilization of a polyhydroxy polymer with boric acid or a boric acid derivative at a mildly alkaline pH. This system is applicable to a broader spectrum of active agents than that of Shasha, supra, but is not suitable for products intended for human ingestion.
Controlled release by means of starch-based encapsulating materials can also be accomplished without the use of chemical crosslinking reactions. In U.S. Pat. No. 2,876,160, Schoch et al. disclose such a method which employs modified, amylose-free starches at concentrations up to 65% solids for embedding water-insoluble materials.
In PCT Int. Appl. WO 85/04074, Flashinski et al. disclose two methods of preparing a starch gel matrix containing an insecticide. The insecticide is either coextruded with a dilute, aqueous dispersion of starch, or the starch is first partially cooked in an extruder prior to cold-blending with the insecticide. In either case, the product is recovered and used as an aqueous gel.
In U.S. Pat. No. 4,230,687, Sair et al. disclose the application of shearing stress, vigorous mechanical working, and heat to distribute active agent into an enveloping matrix of chemically modified starches, gums, and proteins in the presence of a limited quantity of water. Proteins are used for slow-release matrices; modified starches are used for rapid release.
Similarly, in U.S. Pat. No. 3,922,354, Galuzzi et al. disclose the use of high-shear mixing to incorporate active agents into low-water, high-solids matrices prepared from partially gelatinized unmodified starches. Additives such as modified dextrins, mixtures of mono- and diglycerides, toasted cereal solids, and coloring agents are used to control the release of active agents.
In U.S. Pat. No. 3,666,557, Jensen et al. disclose a method of using low-fat starchy materials to microencapsulate individual beadlets of sensitive materials such as vitamins and vegetable oils. Starches are prepared for encapsulation by heating at 88.degree. C. for 30 min followed by passage through a homogenizer to effect disruption of granules without degradation of molecules.
Shasha et al. (U.S. Pat. No. 4,859,377) teach the use of amylose-containing pregelatinized starch to encapsulate entomopathogens, thereby protecting such biocontrol agents from environmental degradation and also promoting infection of target pests. The encapsulation is effected in an aqueous dispersion of the pregelatinized starch: for dry, granular products, the starch solids content of the dispersion is 25-40%; for sprayable liquid products, chemically degraded starch is used at a solids content of 1-10%.
Doane et al. (U.S. Pat. No. 4,911,952) disclose a method for the encapsulation of chemical biological agents using aqueous dispersions of amylose-containing unmodified starch wherein the starch solids content is 20-40% and starch dispersion is accomplished by high-temperature cooking.